This fully automated smart battery charger has three charging modes. Rapid charge mode: Uses the rated maximum charging current to ensure the fastest charging time, the fan of the unit will turn on to ensure the maximum charging current. Silent charge mode (Night mode): Charges at a slightly reduced charge rate without the fan. Maintenance mode: Ideal and recommended for long term battery maintenance. In addition to these three modes, the battery charger has a built-in with overheat and overload electronic circuit protection. When the charger overheats, the charger will decrease the charging current. If temperature is decreased, the charger will resume to normal charging. The charger provides the maximum charging timer management for each charging stage; Once the charger is timed-out, the charger will stop charging to protect your battery and the RED LED will FLASH. The charger also has reverse battery polarity protection. If a reverse battery polarity occurs (Red LED ON, while output leads are connected backwards), simply unplug charger from AC power and properly adjust the connections as described in this manual. If the charger output lead detects a short circuit (Red LED ON, while output leads are connected backwards), simply unplug charger from AC power and properly adjust the connections as described in this manual. Under reverse polarity or short circuit the charger will not deliver any output current.